Addon Packages (langpacks)
The idea behind "langpacks" is to separate translations or language specific content into subpackages in the case that the size of the files is huge or the package is part of a core image that should be minimal.
Subpackages that exist solely to contain additional language translations or content must be named in the format <pkgname>-langpack-<langcode>, where <pkgname> is name of the package the langpacks belong to and <langcode> is a valid language code from /usr/share/xml/iso-codes/iso_639_3.xml or from /usr/share/i18n/locales/. Specifically, the langcode value used in the package name must agree with the langcode identifier used in the directory path by upstream for the translation or language files.
The langpack ecosystem does not need any procedural logic in the form of plugins. Instead it takes advantage of the weak and rich dependency features provided by RPM. The necessary dependencies are computed by the package manager (DNF or PackageKit) so it's crucial to include the following relation in the langpack package definition in the spec file using the Supplements: tag as follows:
Supplements: (%{name} = %{version}-%{release} and langpacks-<langcode>)
Example
Suppose you have a package with following spec file:
Name: php-horde-Horde-Perms ... %files -f Horde_Perms.lang /usr/share/pear-data/Horde_Perms/locale/ ...
In order to create langpacks for each language (/usr/share/pear-data/Horde_Perms/locale/<language>/LC_MESSAGES/Horde_Perms.mo translations), you would need to change the spec file for such language. The snippet below shows the definition of one langpack for bs language by altering the spec file defined above.
Name: php-horde-Horde-Perms ... %package langpack-bs Supplements: (%{name} = %{version}-%{release} and langpacks-bs) %files langpack-bs /usr/share/pear-data/Horde_Perms/locale/bs/LC_MESSAGES/Horde_Perms.mo
%files ...